1. Field of the Invention
The present invention relates to a coaxial cable for transmitting high-frequency signals and, more particularly, to a coaxial cable incorporating improvements in the inner and outer conductors to enhance line speed and to increase cable density in closely arranging a plurality of coaxial cables.
2. Description of the Prior Art
The coaxial cable has been used in most cases for transmitting high-frequency signals because two lines of a simple parallel arrangement increase radiation energy. The coaxial cable, in general, comprises an inner conductor centered inside, an insulating layer coating the inner conductor, an outer conductor coating the insulating layer, and a jacket coating the outer conductor. The coaxial cable is used, for example, for interconnecting a tester for testing the functions of electronic parts, such as ICs and LCDs, and a signal generator that generates testing high-frequency signals. The frequencies of the testing high-frequency signals must be increased to increase the testing speed of such ICs and LCDs, and the density of coaxial cables must be increased to deal with testing electronic parts, such as ICs, having a high degree of integration.
Very fine coaxial cables having very fine inner conductors must be used to arrange the coaxial cables with a large cable density. However, in the conventional coaxial cable, increase in the fineness of the component Cu wire of the inner conductor deteriorates the surface roughness of the inner conductor and, consequently, the waveforms of the high-frequency signals are liable to be disturbed due to skin effect that causes high-frequency signals to be transmitted through the surface of the inner conductor. The disturbance in the waveforms of the high-frequency signals generates noise, which affect adversely the testing function of the tester. Such an adverse effect of the noise on the testing function of the tester increases with increase of the frequency of the testing high-frequency signals. Thus, the conventional coaxial cable is unable to meet both the requirements for the enhancement of testing speed and those for increasing cable density.